Is it true that males are healthier than females but die younger? If so, why? We plan demographic analyses to address these two overarching questions concerning the health-survival paradox. First, to what extent is the paradox true? How general is it? * According to which definitions and measures and along which dimensions are men healthier than women? * How do male-female morbidity and mortality differences vary with age? * How do they vary over place? * How have they varied over time? * How do they vary across species of mammals, birds, reptiles, amphibians and fish? Second, to the extent that the paradox is true, why is this the case? Various social and biological hypotheses will be tested by analyzing: Human and nonhuman lifetables (Project 1); Survey and register data on humans in Denmark (Project 2); Survey data on humans in the United States (Project 3) and in Japan, the Philippines and Singapore (Project 4); Longitudinal observations on baboons in the wild in Kenya (Project 5); Longitudinal data on lemurs in the wild on Madagascar and in captivity at Duke and in France (Project 6);and Laboratory data on fruit flies (Project 7). The combination of informative animal models and high-quality human data and sophisticated demographic analyses will provide a deeper understanding of the basis for sex differences in health and survival and of opportunities to reduce these differences.